There are two ways to get Americans to Mars. One is the way we can afford. The other is the way we can’t. NASA, operating in secret, has been forced to choose the path that will break the bank—the path we simply can’t afford.

NASA is circulating an internal document called “Evolvable Mars Campaign: Status Update to SLS Evolvability TIM.” The pages of the Evolvable Mars Campaign are clearly marked “NASA internal use only—do not distribute.” There may be a reason that NASA is keeping this Mars plan close to the chest. America could never pay for it. It would cost nearly half a trillion dollars–$400 billion, to be specific.

But there’s another way to reach Mars. A way that would cost a mere $40 billion—one tenth the cost of the NASA Evolvable Mars program. As former NASA administrator Lori Garver recently told GeekWire, we could use the private sector. We could put the basic elements of America’s Mars Program up for competitive bids from firms like SpaceX, Orbital Sciences, Sierra Nevada, Virgin Galactic, Jeff Bezos’ Blue Origins, and traditional aerospace big boys like Boeing, Northrup Grumman, and Lockheed Martin. We could use the same sort of fixed-price, commercial contracts that are being used to deliver cargo to the International Space Station.

And we could do one more thing. Stop building expensive rockets you throw away after one use. Build rockets to be launched over and over again—the way we reuse passenger planes, trucks, and trains. The result? According to the Space Development Steering Committee’s chief analyst John Strickland and to former Apollo program rocket scientist and GE aircraft engine specialist Gerald Black, also of the Space Development Steering Committee, you could have a Mars program that would fit entirely within NASA’s current budget.

What’s wrong with NASA’s Evolvable Mars Campaign? Expendability. Throwing expensive rockets away. The Evolvable Mars Campaign requires 22 flights of a rocket designed by Congress to generate jobs, the Frankenrocket, the Space Launch System. And it calls for as many as three launches of the SLS per year.

Points out the Space Development Steering Committee’s Gerald Black, “with the current budget NASA can only afford at most one SLS flight every two years.” Adds Black, “The first two SLS flights are likely to occur 4 or 5 years apart according to the latest NASA schedule. Both the NASA Advisory Council and the Aerospace Safety Advisory Panel have been warning that this flight rate is insufficient to maintain the proficiency of the launch crew.” How would NASA solve these Space Launch System problems? Says Black, “with a large infusion of funds.” Adds Black, those funds are unobtanium: “A lot of smart and knowledgeable people have been warning that such an increase in NASA funding is unlikely to occur.”

In addition, the Evolvable Mars Campaign relies on the Orion Capsule. Says Black, the SLS and the Orion have been, “Developed by NASA using cost-plus contracts,” the sort of contracts that jack up the price of military aircraft toilet seats from $17 to $700. The result, says Black, is that the costs on the SLS and Orion “are out of control and their schedule has been slipping.” Concludes Black, “If NASA uses its traditional cost-plus contracts for all the other yet to be developed hardware components, the cost of the Evolvable Mars Campaign will rocket into the stratosphere.”

Is there an alternative? You bet. The one hinted at by Garver. Use competitive bids and fixed price contracts. Harness the creativity of the private space industry. Or as Black puts it:

Instead of the Space Launch System, a commercial Super Heavy Lift Vehicle should be used. Fortunately, SpaceX is already developing such a launch vehicle. SpaceX hasn’t come up with an official name for this launch vehicle yet. However, some people have been calling it the BFR, for Big Falcon Rocket (or Big Fu….g Rocket). This rocket will have significantly more payload capability than the SLS. Unlike the fully expendable SLS, the BFR is designed to be fully reusable, a trait that could eventually lower the cost two orders of magnitude—99%– below that of the SLS.

In other words, for the cost of one SLS launch, you might be able to launch as many as 100 SpaceX BFRs. But there’s more. Explains Black,

The BFR is one element of the Mars Colonial Transporter (MCT) system that SpaceX is developing. SpaceX officials have claimed that this system will be able to land 100 people or 100 tons of cargo on Mars. This is considerably more capability than the SLS and the other elements of the Evolvable Mars Campaign can deliver. We don’t know the details of the MCT system yet, but Elon Musk (the CEO of SpaceX) has said he “hopes” to release details of this system and a new architecture for human missions to Mars by the end of this year. The MCT system could form the core of a humans to Mars plan.

Instead of the Orion spacecraft, a much cheaper commercial spacecraft should be used. Possibilities include SpaceX’s Dragon 2 capsule or Boeing’s CST-100 Starliner capsule, both of which will be carrying crew to and from the ISS as part of the Commercial Crew program. Sierra Nevada’s Dream Chaser is another possibility. SpaceX’s Dragon 2 is being designed with beyond earth orbit missions in mind. It has many advantages over Orion, including a more advanced heat shield, a more advanced abort system, the ability to touch down on land with pinpoint accuracy, and about an order of magnitude lower cost.

But America has more private sector options to offer. Back to Black:

Other commercial companies could also contribute to the Mars effort. Bigelow Aerospace could supply inflatable habitat modules for use in transit to Mars and as surface habitats on Phobos and Mars. More established aerospace companies like Boeing, Lockheed Martin and Northrup Grumman could compete for the contracts also. International partners could also contribute to the effort, further reducing the cost.

The point is that, by fully using the resources of the commercial space industry, a humans to Mars program could be accomplished for about one-tenth the cost of NASA’s proposed Evolvable Mars campaign. Instead of costing around $400 billion, it might cost around $40 billion.

And here’s the real secret. The private-sector alternative, concludes Black, would do something magical. It “would be affordable within the current NASA budget.” In other words, the film the Martian is not just science fiction. If we harness the private space industry, we CAN afford to get to Mars.